When the US govt printed money in 2008 and lend it to the banks, how much the banks had to pay in interest?
Quantitative Easing is the purchase of bonds by the central bank. The purchases leave private banks with balances at the central bank (reserves). The private banks are “lending” the Fed money (not that it needs it). The rate if interest paid is set by the Federal Reserve.
The rate paid is shown at: Link to FRED seeies.
(Note that some balance sheet expansion was repurchase agreements - repos - which are a matched pair of transactions where the Fed buys a Treasurybond, then sells it back at a pre-determined price. This can be interpreted as a loan, with an implied interest rate - the repo rate. These are “open market transactions,” and the exact details are not publicly disclosed. However, the repo market is a large market, and repo trades near the Fed Funds rate, as both represent lending backed by the Federal government.)